This invention relates to captivated jackscrews, and, more particularly, to a new, more rugged and improved captivated jackscrew design.
Mating or connecting two metal panels or frames together is easily accomplished with standard fastener""s, such as machine screws. For that, one of the panels includes a clearance hole which allows the machine screw""s threaded shaft to pass through, but not the screw head. The screw is then screwed into an associated threaded hole formed in the second panel. Another elementary alternative to the foregoing is the conventional bolt and nut arrangement. The bolt is extended through drilled clearance holes in the two metal panels and a threaded nut is threaded onto the bolt shaft and tightened, compressing the panels between the bolt head and the nut.
If for any reason some time later one wishes to detach the two panels, one may discover that detachment may not be as easy. Assuming one is successful in removing the machine screws and/or nut and bolts, one may find that the two metal panels remain stuck together. Over the years corrosion, metal migration, electrical corrosion or the like, or for other reasons, hereafter described, may have occurred between the two metal panels or frames form an additional binding, which must be broken to detach the two, often requiring great force and/or leverage. One finds it""s very difficult or near impossible to separate the two panels.
The captivated jack screw was designed to avoid the problem of separating metal sheets where such circumstances are anticipated. The conventional jackscrew, which the present invention improves upon, includes a narrow slot peripherally extending about the screw""s shaft, a reduced diameter shaft portion in the machine screw""s shaft, located at an axial position below the screw""s head, typically by a distance equal to the thickness of the panel, and an E-clip, a somewhat U-shaped flat spring steel member that fits into that reduced diameter slot. The machine screw""s shaft is extended through the hole in the panel member, leaving the screw""s head on one side of the panel, unable to pass through the hole, and positioning the narrow slot on the other side of the panel member. The e-clip is forced into place laterally in the narrow slot, its arms, under the spring force, gripping the shaft.
The e-clip is larger in size than the panel""s screw hole. Hence, the clip prevents the machine screw from being withdrawn from the hole. In effect, the screw is captured on the panel, and cannot fall off. Further, the e-clip does not prevent rotational movement of the screw shaft, the shaft and e-clips may rotate as a set within the panel or independently. With the screw thus captured, using a machine screw driver, the screw""s threaded shaft is screwed into the threaded hole in the second panel. When the screw is tightened, the two panels are fastened together with the sides of the e-clip in between and generally located in a small recess in either panel. The clip does not contact either panel when the two are fastened together.
To then later detach the panels, the machine screw is turned in the opposite direction than before, counterclockwise, for example, withdrawing the screw from its mating threaded hole in the second panel. As the screw""s shaft axially moves out of that threaded hole, the shaft in turn moves the reduced diameter portion in which the e-clip is fixed, but permitting clip rotation, and, hence, also carries the e-clip axially out with the shaft. Since one side of the clip abuts the underside of the first panel, the clip, which is fixed in axial position on the screw shaft, is forced by the screw shaft to push the first panel away from the second. Those familiar with the screw type jack used to raise a home off its foundation easily recognize that in separating the two panels, the foregoing screw and e-clip structure forms a jack arrangement, wherein the side of the e-clip serves as the jack""s table. The screw type jack obtains a mechanical advantage, multiplying the smaller torque required to rotate the screw threads to a larger force exerted along the axis of the screw shaft. Ideally such a force breaks any naturally formed binding between the panels. In reality its functionality is limited.
Captivated jackscrews have served in many applications. As example, although the foregoing description describes one example of the captivated jack screw""s use in connecting two panels, it also serves to mate or join mating male and female multi-contact electrical connectors and to de-mate those connectors. Typically multi-contact electrical connectors are used to join the many electrical wires within an electrical cable or on one electrical component to a mating electrical connector on electrical equipment, placing the wires into the proper electrical circuits within the equipment. Those connectors are typically fastened together with clips or screws, and some of the latter may be captivated jack screws.
With higher quality connectors to ensure reliable electrical connections, the female contacts in a connector are designed to grip the associated male contacts of the other connector with a significant force. With large numbers of such contacts the total force required is quite large. This gripping action produces a binding between the mating connectors. Thus, great force is required both to mate or fully insert one connector into its mate and, later, to demate or separate the connectors. With the captivated jackscrew arrangement, unscrewing the machine screw pushes one connector away from the mating connector to perform de-mating disconnection, minimizing the user""s effort. This feature is particularly helpful if the connectors are located in places that are difficult to access or difficult to grip by hand, and especially in applications in which mating and de-mating of the connectors is required frequently.
Although of simple and inexpensive structure, the e-clip and necked machine screw design attains a functional limit as a jack when the binding forces are quite large. First, the xe2x80x9cneckedxe2x80x9d design for the machine screw in which the screw shaft is modified to contain a constricted diameter portion, weakens the screw shaft. Inadvertently exceeding the torque applied to the screw during the jacking operation could break the shaft and cause an expensive and time consuming on-site repair. More likely, the overly great forces applied to the sides of the e-clip during the jacking operation causes this thin spring steel member to twist and distort its geometry, withdrawing the ends thereof from the neck in the machine screw holding the e-clip in place on the screw. With those gripping ends released, the e-clip comes free. Once released from the fastener shaft, it may be exceedingly difficult to separate the two panels.
As an advantage, the present invention does not employ such frail clips and is able to handle greater torques than the foregoing e-clip design. It also avoids the necessity of necking the machine screw and weakening the screw shaft, making use instead of a standard, unmodified fastener.
Accordingly, a principal object of the invention is to provide a more rugged and reliable captivated jackscrew design, one that can handle greater loads than existing e-clip designs.
A further object of the invention is to provide a captivated jackscrew design that uses a standard fastener, such as a machine screw, avoiding the necessity for xe2x80x9cneckedxe2x80x9d screws and concomitant weakening of the machine screw shaft.
In accordance with the foregoing objects and advantages, the novel captivated jackscrew of the present invention is characterized by the formation of an internal cavity within one of the two bodies that are to be connected together and an access passage to that cavity; one end of the cavity, located at one end of the body is open, and the access passage extends through the other end of the body into the other end of that cavity. A standard machine screw is installed head first within the cavity, with the screw shaft, being of greater length than the cavity, protruding from the end of the body. A barrier is provided to prevent withdrawal of the machine screw head, but permit the screw head and shaft to move a limited distance axially.
In the preferred embodiment, the screw head is oriented in the cavity to permit a screw driver, such as an Allen wrench, to access the screw head through the access passage. In a second less preferred embodiment the screw shaft, being greater in length than the access passage, is positioned extending through and beyond the end of the access passage; and driver access to the machine screw head is provided through the barrier.
In another specific aspect to the invention, a portion of the internal cavity walls contains a screw thread and the barrier is of a cylindrical shape containing mating screw threads along the outer wall and a central passage there through. The diameter of that central passage is smaller than the head of the machine screw. The barrier is thus screwed into place plugging the open end of the cavity and xe2x80x9ccaptivatingxe2x80x9d or preventing withdrawal of the screw head.
In yet another specific aspect of the invention a backstop is included in the cavity adjacent the end containing the access passage. The backstop prevents the machine screw head from rubbing directly against the body, particularly the end wall of the cavity.
The foregoing and additional objects and advantages of the invention together with the structure characteristic thereof, which was only briefly summarized in the foregoing passages, and equivalents thereto becomes more apparent to those skilled in the art upon reading the detailed description of a preferred embodiment, which follows in this specification, taken together with the illustration thereof presented in the accompanying drawings.